The search for justice in the death of Michael Brown, the black unarmed teenager killed in Ferguson, Missouri, will eventually move away from the streets and into the courtroom.

Darren Wilson, the police officer who killed Brown on August 9, could stand trial for his actions. St. Louis County is conducting a criminal investigation.

When that is completed, county prosecutors will determine whether to charge Wilson with a crime—Reuters reported that the case could be given to an investigating grand jury as early as this week to decide whether Wilson will be indicted.

If Wilson is charged, the question will no longer be about the frayed race relations in St. Louis and its environs, the frequency with which police kill unarmed black men, or the militarization of America’s police forces. The question will be: Did Wilson kill Brown legally?

More facts about what happened on that fateful Saturday afternoon will likely come to light. Right now, accounts from eyewitnesses, police and a friend of the officer involved give different accounts with different legal implications.

What we know—and don’t know

Witnesses and police have different versions of the events that led up to Brown being shot dead. Both the St. Louis County police and the FBI, as well as the Civil Rights Division of the Department of Justice, are investigating what happened.

According to what is known so far, at 12:01 pm on Saturday, August 9, Brown and a friend, Dorian Johnson, were walking down the middle of Canfield Drive, a residential street in Ferguson, when a police car pulled up near them. The officer in the car, Darren Wilson, ordered the two young men to move to the sidewalk.

According to the account of the St. Louis County police, Wilson attempted to get out of his car and Brown pushed him back inside. A struggle ensued inside the car, in which Brown tried to take the officer’s gun. A shot was fired from inside the car. The officer then stepped out of the car and shot Brown, who died of his injuries.

But eye witnesses, including Johnson, tell a different version of events. According to Johnson, after Officer Wilson told the two men to get on the sidewalk, he slammed his brakes, put his car into reverse, and attempted to open the door of his police car. The door hit Brown and then bounced shut again. In an interview with MSNBC last week, Johnson described how Wilson reached out and grabbed Brown by the neck. The altercation became like a “tug-of-war,” with Wilson trying to pull Brown inside the car and Brown pulling away.

Wilson fired off a shot which Johnson said hit Brown. The two young men began running away. After another shot or more was fired, Johnson said his friend turned around with his hands raised in the air and said, “I don’t have a gun, stop shooting!” The officer, then facing Brown, fired several more shots and Brown fell to the ground.

A second eyewitness, Piaget Crenshaw, who saw the events from her apartment and videotaped the aftermath, told CNN that she saw Brown and the officer struggle and that it looked like the officer was trying to pull Brown into the car. When that didn’t work, she said the officer chased after Brown and shot multiple times, though none of those shots appeared to hit Brown. In the end, Crenshaw said, Brown “turned around and then was shot multiple times.”

After St. Louis County performed an initial autopsy, the Brown family lawyer hired a veteran medical examiner, Dr. Michael M. Baden of New York, to do a second autopsy because of doubts about whether the police investigation would be fair. According to theNew York Times, Baden’s autopsy showed that Brown was struck at least six times and that the bullets entered from the front of his body. The Justice Department announced Sunday that they would take the unusual step of performing a third autopsy.

About 10 minutes before Brown and Johnson were stopped by Officer Wilson, video footage released by the police last week showed the two young men taking cigars from a convenience store—footage that enraged the Ferguson community, which saw the release of the video as an attempt to smear the dead teenager. The Ferguson police later clarified that Wilson did not know that Brown was a suspect in a robbery when he approached the two young men for walking in the middle of the street.

Much of the legal case will hinge on what new facts come to light and what forensic evidence will reveal about exactly what took place that fateful day.

Wilson’s side of the story

On Monday, Officer Wilson’s side of the story emerged for the first time. A friend of the officer called into a radio show to tell the story and a source confirmed to CNN that it matched the version of events Wilson gave investigators.

In that version, told by a woman who identified herself as “Josie,” Wilson asked the two men to get on the sidewalk. He then heard a report of the robbery and a description of the suspects, which matched Brown and Johnson. When Wilson then tried to get out of his car, Brown pushed him back in and punched him in the face, and then reached for his gun. The two tussled, Brown had the gun pointed at Wilson’s hip, but Wilson pushed it away before it went off in the car.

The two men then began to flee and Wilson gave chase, ordering them to stop, Josie said. In her account, Brown then turned around and began to taunt Wilson, saying he would not shoot them. Then Brown charged at Wilson at full speed, at which point Wilson opened fire.

“All of the sudden, [Brown] just started to bum rush him,” Josie told radio host Dana Loesch. “He just started coming at him, full-speed, and so [Wilson] just started shooting, and [Brown] just kept coming.”

“So [Wilson] really thinks [Brown] was on something, because he just kept coming. It was unbelievable.”

Did Wilson act “reasonably”?

"Did the police officer have a reasonable fear either for his own safety or the safety of others?"

That, according to Peter Joy, a criminal justice expert at the Washington University School of Law in St. Louis, is the central question in cases like this. “It's a question of, 'Was it reasonable to act in the way the police officer did?' Being reasonable would be triggered by, 'Is there a reasonable risk of harm?'"

Whether or not the police officer knew Brown was unarmed when either fleeing or surrendering becomes important here. “Assuming the answer [is] he knew he was unarmed, I think that, by itself, would mean no justification for the shooting,” Joy said.

According to Dorian Johnson, the friend who was accompanying Brown and witnessed the shooting at close quarters, Brown said out loud he was unarmed before Wilson fired the final deadly shots.

“If he was trying to surrender and the police officer knew he was unarmed—or even if he was armed, if he’s trying to surrender—then at least the police should tell him to unarm himself or have him stay there with his hands up and call for backup,” Joy said. Joy stressed that the ultimate verdict will depend on how the facts unfold.

The version of events told by Wilson’s friend gives Wilson a more reasonable fear for his safety than the accounts of other witnesses thus far.

“Speaking hypothetically, if there was a physical confrontation and if he reached for the officer's gun... then if he charged at the officer, those facts put together would strengthen the police officer's self defense claim," said Jens David Ohlin, a criminal law professor at Cornell University Law School. "Each one in isolation might not be enough...they are the building blocks for a self-defense claim."

Ohlin added that the accusation of charging might not ultimately be as important as Josie’s claim that Brown tried to get the officer’s gun. “The charging by itself doesn't indicate necessarily a risk to the officer's life, but a suspect reaching for the gun of a police officer, that potentially puts the police officer's life in jeopardy," he said. Whether or not that actually happened is “an incredibly important piece of the puzzle."

“This account is another illustration of the fact that we don't know what happened,” Joy said. If it turns out that Josie’s account is what happened, he added, “it could support the position that the officer was in fear for his safety and the safety of the community when he shot and killed Mr. Brown. He could have been thinking that if he didn't stop him, Mr. Brown might be able to take his gun and use it on him or possibly use it to harm others.”

The “reasonable” standard often gives the benefit of the doubt to police in these circumstances. They need not actually be in danger, only reasonably believe that they are—a subjective standard. Moreover, the courts often give deference to police, whose job is to protect the public and make snap judgments in dangerous and high-pressure situations.

The fleeing felon

"At one point in American history it was not uncommon for state law to permit officers to use deadly force to apprehend a fleeing felon," said Frank O. Bowman III, criminal law professor at University of Missouri School of Law. Those state laws made it easier for police officers (often white) to shoot fleeing suspects (often black) without repercussions.

But in 1985, the Supreme Court declared in Tennessee v. Garner that police cannot use deadly force to stop a fleeing felon who is not perceived to be dangerous.

In the Garner case, a Memphis police officer responded to a report of a home burglary and, once at the scene, saw a figure dash across the backyard. Using his flashlight, the officer could see that the figure was a teenager who appeared to be unarmed.

The officer ordered the suspect to halt. When the teen instead tried to flee by climbing a fence, the officer shot and killed him. That fleeing felon turned out to be 15-year-old Edward Garner. He was 5’4”, about 110 pounds, unarmed, and black. He had on him a purse and $10.

A majority of the Supreme Court held that in order to use deadly force against a fleeing felon, the police must have probable cause to assume that the felon poses a significant risk of harm to the officer or the community. The shooting of Garner was, therefore, unconstitutional.

How does this affect the case of Michael Brown? Until Josie shared Wilson’s account, the known facts indicated that Brown was either fleeing or surrendering when he was shot. Assuming he was fleeing or surrendering, not charging, the facts that would suggest it was likely illegal to shoot Brown.

It’s unclear at this point whether Darren Wilson knew that Brown was suspected of robbing a convenience store. If he didn’t know, then the robbery plotline is, as Joy put it, a “red herring.” If he did realize the two were suspects, it’s possible he thought they were therefore dangerous, even though no weapon was used in the “strong-arm” robbery, as police are calling it.

What if Brown did assault Wilson and try to take his gun before fleeing—the account put forward by the St. Louis County police? Would that make him a dangerous fleeing felon?

“It’s conceivable that there might be a determination that Mr. Brown had committed an assault that was equivalent to a felony against a police officer and that might be viewed legally as a justification for the use of force—and in this instance, deadly force,” Joy said.

But assuming Brown didn’t charge at Wilson, as his friend recounted, other legal experts say that argument would be shaky at best.

Assuming "that Brown breaks away from the police officer and the police car, is not armed, and is at some distance away from him—not presenting any immediate threat to the officer or anybody else—then it's plainly illegal to shoot him,” said Bowman.

Did a struggle with the police officer turn Brown into a violent fleeing felon? After all, police department’s account claims Officer Wilson’s face was hit during the altercation and he was treated for his wounds at a hospital.

Not according to Bowman. “If you’re a police officer and I walk up and punch you in the nose and turn around and run away, you can’t pull out your glock and shoot me in the back. You just can’t. The law insists on far more restraint than that from police officers.” he said.

Generally, the law requires more than an altercation to justify the use of deadly force against someone who is fleeing the police, like assaulting an officer with a deadly weapon, or committing a crime with a deadly weapon.

“It’s pretty hard to think of any legal justification for the officer firing at this guy once contact is broken and the guy is moving away,” Bowman said.

Bowman was a little wary of Josie’s account, but stressed that an investigation will have to sort fact from fiction. “The idea that, once out of the car, the kid would then charge an obviously armed policeman seems to me less probable,” he said. “But, who knows? We'll see what the actual investigation decides.”